1. Field of the Invention
This invention relates to a combination of pour point depressants formulated into petroleum lubricants containing waxy or wax-like components and ethylene-copolymeric viscosity index improving agents. More particularly, this invention is concerned with a mixture of an oil-soluble, condensation product of chlorowax/naphthalene and a second pour point depressant of the class of a polymer of an ester of acrylic acid or methacrylic acid and a monohydric alcohol containing from about 10 to about 18 carbon atoms and/or an interpolymer obtained from a mixture of a vinyl alcohol ester of a C.sub.2 to C.sub.18 alkanoic acid and a di(C.sub.6 -C.sub.18 alkyl) fumarate whereby the low temperature performance of lubricating oils blended from light and heavy petroleum components with a viscosity index improving amount of an ethylene copolymeric viscosity index improving agents are materially improved.
Present day motor oils for the lubricating of internal combustion engines are usually petroleum or mineral oils of suitable viscosity compounded with one or more addition agents to impart various desired properties thereto.
Among the usual addition agents employed are socalled detergent type additives and viscosity index (V.I.) improvers, the latter being used to modify the viscosity-temperature characteristics of the oil. Such types of V.I. improvers included the oil-soluble polymerization products of an ester of acrylic acid or its alpha-alkyl substitution products and monohydric alcohols containing more than 4 carbon atoms preferably from about 4 to about 18 carbon atoms, (see U.S. Pat. Nos. 2,091,627, 2,100,993 and 2,407,954).
Other known V.I. improvers include polyisobutylene, copolymers of vinyl esters and fumaric acid esters, alkyl styrenes and copolymers of styrene and alkenes or alkylidenes, acrylate and methacrylate esters with and without nitrogen-containing esters. Highly useful V.I. improving agents are polymers of ethylene and C.sub.3 to C.sub.18 olefins. Examples of these copolymers, made with the aid of Ziegler-Natta catalysts are described in U.S. Pat. Nos. 3,522,180, 3,551,336 and 3,697,429.
The term "pour point" is used to denote the lowest temperature at which an oil will pour or flow when chilled without disturbance under specified conditions. The pour point of a refined lubricating oil was previously believed of practical importance in order to avoid problems of engine lubrication at low temperatures.
At the present time, the pour point test (ASTM D-97) is generally recognized to be deficient in predicting operation preformance.
It is known to use combinations of pour depressants in lubricating oils for U.S. Pat. No. 2,916,447 teaches that octane requirement of a spark ignition internal combustion engine can be reduced by incorporating from about 0.5% to about 10% of a condensation product of a long chain chlorinated alkyl hydrocarbon of from about 10 to about 50 carbon atoms and a mono- or dinuclear aromatic compound into a motor oil containing from about 0.5% to about 15% of an oil-soluble polymer of an ester of acrylic acid or of its alpha-alkyl or alpha-phenyl substitution products and a monohydric alcohol containing from 4 to about 18 carbon atoms, and from about 0.5% to about 10% of a neutralized polyvalent metal-containing phosphorus- and sulfur-containing detergent additive.
Frequently it is found that the presence of V.I. improver additives in conventionally-formulated lubricating oils undesirably raises the pour point of the lubricating oil to a point which renders the oil less than fully satisfactory at low temperature. This appears to occur, at least in part, because the VI improvers employed interfere with the operation of conventional lubricating oil pour point depressants.
Such a low temperature difficulty involving ethylene copolymeric V.I. improvers was overcome in U.S. Pat. No. 3,697,429. It is taught therein that a low pour, solvent-refined, midcontinent lubricant base stock containing an additive package, including a mixture of the condensation product of naphthalene and chlorinated wax and the condensation product of di(C.sub.8 -C.sub.18 alkyl) fumarate and vinyl acetate, can be usefully viscosity modified with an ethylene-propylene copolymeric mixture of high and low ethylene content copolymers.
It is an object of this invention to provide a system which permits attainment of improvement in viscosity index of lubricating oils of high wax content particularly those blended from light and heavy petroleum components (distillation cuts and extracted residues).